Visceral adipose tissue loss and 24-hour urinary profile changes post-bariatric surgery

The relationship between obesity and nephrolithiasis is a well-documented phenomenon. Visceral adipose tissue (VAT) has been proposed to be an accurate indicator of metabolic derangement. We present a study that investigates the relationship between computed tomography (CT) delineated VAT measurements and 24-hour urine (24 HU) profiles in the context of profound weight loss.

A total of 86 patients with a history of nephrolithiasis who underwent bariatric surgery were reviewed. All patients had pre and postoperative 24 HU analysis and CT kidney and urinary bladder performed. CT-based fat delineation program, AnalyzePro, was used to measure VAT at levels L4-L5 (VAT 1) and L1-L2 (VAT2). Univariate and multivariate analysis was utilized to examine associations between VAT measurements and comorbidities, 24 HU values, and postoperative urinary changes.

Preoperative VAT2 was correlated with preoperative serum creatinine and all 24 HU (R2: 0.23-0.43, p = < 0.001-0.030). Only VAT1 and VAT2 had relationships with hypertension, dyslipidemia, and metabolic syndrome (R2: 0.25-0.30, p = 0.004-0.015). The percent change in VAT1 and VAT2 was a significant predictor of change in 24 HU uric acid (respectively, R2: 0.14, beta: -0.03, p = 0.002 and R2: 0.13, beta: -0.03, p = 0.003).

This study found VAT to have strong correlations with urinary outcomes in obese patients, especially in the excretion of uric acid. These findings support a potential use of CT delineated measurements of fat as a surrogate measure for urinary metabolites, and may be used as a marker for patient counseling in stone prevention.